Large Delay Variation Research Articles

Variation-Aware Global Placement for Improving Timing-Yield of Carbon-Nanotube Field Effect Transistor Circuit

As the conventional silicon-based CMOS technology marches toward the sub-10nm region, the problem of high power density becomes increasingly serious. Under this circumstance, the carbon-nanotube field effect transistors (CNFETs) emerge as a promising alternative to the conventional silicon-based CMOS devices. However, they experience a much larger variation than the silicon-based CMOS devices, which results in a large circuit delay variation and hence, a significant timing yield loss. One of the main variation sources is the carbon-nanotube (CNT) density variation. However, it shows a special property not existing for silicon-based CMOS devices, namely the asymmetric spatial correlation. In this work, we propose novel global placement algorithms to reduce the timing yield loss caused by the CNT density variation. To effectively reduce the statistical circuit delay, we first develop a statistical delay measure for a segment of gates. Based on this measure, we further develop a segment-based strategy and a path-based placement strategy to reduce the delays of the statistically critical paths. Experimental results demonstrated that both of our approaches effectively improve the timing yield.

Use of Phase Delay Analysis for Evaluating Wideband Circuits: An Alternative to Group Delay Analysis

A phase delay analysis is proposed against pursuing a flat group delay response for the design of wideband circuits. While it is believed that a large group delay variation introduces a large data-dependent jitter, this brief reconsiders the effectiveness of the group delay analysis in the evaluation of wideband circuits. Because of its own differentiating nature, the group delay provides a good insight on the delay variation at a vicinity of a certain frequency. However, for certain kind of wideband circuits, the group delay analysis cannot provide a sufficient insight since much of useful information is lost or distorted during the differentiating operation. In this brief, the effectiveness of the phase delay analysis is investigated and comparison with a traditional group delay analysis is presented with a theoretical approach and through a few circuit examples.

A CSMA-based MAC protocol for WLANs with automatic synchronization capability to provide hard quality of service guarantees

The carrier sensing multiple access with collision avoidance (CSMA/CA) protocol is a widely-adopted MAC protocol in the current wireless networks, but the quality of service (QoS) cannot be guaranteed due to random access. Investigations reveal that the collision avoidance mechanism which relies on the binary exponential backoff scheme is the root cause of QoS issue. Therefore, this paper first proposes a CSMA with automatic synchronization (CSMA/AS) MAC protocol to mitigate the collision problem caused by random access. By CSMA/AS, all the stations can be synchronized and then served in a round-robin fashion without contention collisions. Even if a new station joins, the wireless network can also quickly converge and go back to the synchronized state. The simulation results show that the proposed CSMA/AS protocol can fully mitigate the issues caused by random access, such as the severe contention collisions and large delay variation. In addition, this paper demonstrates how to provide hard QoS guarantees, such as fairness, rate guarantee, and delay guarantee, which cannot be achieved by the existing CSMA-based protocols. Because CSMA/CA does not rely on any additional control message, the implementation complexity of CSMA/AS is similar to that of legacy CSMA/CA protocols.

Towards Temperature Insensitive Nanoscale CMOS Circuits with Adaptively Regulated Voltage Power Supplies

In this paper, we show that the temperature-induced performance drop seen in nanoscale CMOS circuitscan be tackled by powering the circuits with adaptively regulated voltage power supplies. Essentially, when temperature rises, the supply voltage will be bumped up to offset otherwise performance degradation. To avoid thermal over-drift as chip temperature exceeds its operation range, a voltage limiteris integrated into the proposed power supply to cap the supply voltage. Using this proposed adaptive voltage source to power individual CMOS logic gates and/or subsystems will free the chips from using expensive high-precision temperature sensors for thermal management and performance tuning. Experiments on various benchmark circuits, which are implemented with a 45nm CMOS technology, have confirmed that the circuit delay variation can be reduced to 15%~30% over a wide temperature range (0℃ to 90℃), a sharp contrast to the large delay variations (50%~75%)observed in most IC designs where a constant power supply is employed.

Towards Temperature Insensitive Nanoscale CMOS Circuits with Adaptively Regulated Voltage Power Supplies

In this paper, we show that the temperature-induced performance drop seen in nanoscale CMOS circuitscan be tackled by powering the circuits with adaptively regulated voltage power supplies. Essentially, when temperature rises, the supply voltage will be bumped up to offset otherwise performance degradation. To avoid thermal over-drift as chip temperature exceeds its operation range, a voltage limiteris integrated into the proposed power supply to cap the supply voltage. Using this proposed adaptive voltage source to power individual CMOS logic gates and/or subsystems will free the chips from using expensive high-precision temperature sensors for thermal management and performance tuning. Experiments on various benchmark circuits, which are implemented with a 45nm CMOS technology, have confirmed that the circuit delay variation can be reduced to 15%~30% over a wide temperature range (0℃ to 90℃), a sharp contrast to the large delay variations (50%~75%)observed in most IC designs where a constant power supply is employed.

A Nonlinear Predictive Controller Based on Chaos Optimization Apply to Reheated Steam Temperature

In the power plant reheat steam temperature control system with large time delay, large inertia and dynamic variation of uncertainty, a new nonlinear predictive controller is proposed which combines neural network identification, chaos optimization algorithm (COA) and the concept of predictive contro1. The controller utilizes neural network as predictive model and COA as online optimization. It can avoid calculating the complicated gradient and the inverse matrix in the nonlinear predictive control. The simulation studies show the effective performance of the proposed controller.

Identification-Free Adaptive Separate Layer Water Injection Control Based on Expert Amendment

An identification-free adaptive control strategy based on expert amendment is proposed in this paper to solve the problem that it is difficult to establish mathematical model of water injection regulating process due to large time delay, strong nonlinearity and time variation in the flow control of separate layer water injection technology. In this control strategy, according to the past and current process information of water injection, the system output and trend can be estimated based on expert rules to amend the output of the identification-free adaptive control. The simulation result shows that this control strategy has perfect control performance and strong adaptability and it provides a feasible means for improving water injection effect.

Feedforward model predictive control of a non-linear solar collector plant with varying delays

This study discusses non-linear optimal feedforward control of solar collector plants. The control problem is challenging, with non-linear disturbance effects and long input-dependent transport delays. The controller operates in a model-based predictive control framework, without feedback and constraints, to highlight feedforward controller performance gains. To reduce the computational complexity state extension is avoided when modelling the time delays. The motivation for this is provided by a proof of the equivalence between state extension and direct prediction in optimal control, for non-linear multiple-input-multiple-output (MIMO) systems with time delays in disturbances and controls. The solar collector controller also uses flow-dependent sampling to reduce the time variation of the delays. To obtain an accurate model for feedforward controller design, a black-box recursive prediction error identification algorithm was used for modelling of the non-linear plant using measured data. Experimentally, accurate feedforward control was obtained when the controller design was tested with simulation, using measured disturbances from the plant. About two-thirds of the control effort needed appears to be available by feedforward control only. In order to evaluate the algorithms in difficult conditions, the evaluation was performed on data obtained during a day with partly cloudy weather. This caused large flow variations, and consequently large time delay variations.

Synctium: a Near-Threshold Stream Processor for Energy-Constrained Parallel Applications

While Moore's law scaling continues to double transistor density every technology generation, supply voltage reduction has essentially stopped, increasing both power density and total energy consumed in conventional microprocessors. Therefore, future processors will require an architecture that can: a) take advantage of the massive amount of transistors that will be available; and b) operate these transistors in the near-threshold supply domain, thereby achieving near optimal energy/computation by balancing the leakage and dynamic energy consumption. Unfortunately, this optimality is typically achieved while running at very low frequencies (i.e. 0:1 - 10 MHz) and with only one computation executing per cycle, such that performance is limited. Further, near-threshold designs suffer from severe process variability that can introduce extremely large delay variations. In this paper, we propose a near energy-optimal, stream processor family that relies on massively parallel, near-threshold VLSI circuits and interconnect, incorporating cooperative circuit/architecture techniques to tolerate the expected large delay variations. Initial estimations from circuit simulations show that it is possible to achieve greater than 1 Giga-Operations per second (1GOP/s) with less than 1 mW total power consumption, enabling a new class of energy-constrained, high-throughput computing applications.

Robust On-Chip Signaling by Staggered and Twisted Bundle

Existing shield insertion for multiple signal nets can lead to a nonuniformly distributed, capacitive-coupling length and inductive return paths, introducing large delays and delay variation by crosstalk. This article discusses a twisted, staggered interconnect structure that reduces both inductive and capacitive crosstalk. The proposed design reduces delay by 25% and reduces delay variation by 25times compared to designs employing coplanar shields.

On Window Control Algorithm over Wireless Cellular Networks with Large Delay Variation

In addition to high bit error rates, large and sudden variations in delay often occur in wireless cellular networks. The delay can be several times the typical round-trip time, which can cause the spurious timeout. In this letter, we propose a new window control algorithm to improve TCP performance in wireless cellular networks with large delay variation and high bit error rates. Simulation results illustrate that our proposal improves the performance of TCP in terms of fairness and link utilization.

Complex upper-mantle deformation beneath the North China Craton: implications for lithospheric thinning

Summary The mechanism of lithospheric thinning of the North China Craton (NCC) remains controversial. To constrain the mechanism, this study investigated the upper-mantle deformation pattern of the craton by measuring shear wave splitting at the cratonic edge. The results, derived from data recorded at 47 stations, reveal a complex pattern of mantle deformation. Inside the eastern craton, the majority of fast direction trends SE—NW parallel to the tectonic extension direction accompanying with the lithospheric thinning. At the cratonic edge, 15 stations with only null splitting results indicate undetectable anisotropy beneath the stations. This may be due to upwelling or chaotic ascension of mantle flow. To the north, off the craton, large delay times and variation of splitting parameter with backazimuth are generated by the combination of lithospheric and asthenospheric anisotropy. Based on comparison of the splitting results and the predicted ones by the compelling models, it is likely that lithospheric delamination dominated the lithospheric thinning at the north edge of the NCC during the Mesozoic to Cenozoic.

Q-Soft: software framework for QoS support in home networks

In this paper we report the development and implementation of Q-Soft, a Quality of Service (QoS) software framework, that provides QoS support for real-time (RT) applications in wired and wireless home networks. RT applications such as voice and video are delay and delay variation sensitive, i.e., in case the packets incur large delays and delay variation, the quality of the application is severely degraded (e.g., the video is choppy and the voice is not clear). Successful launching of RT applications necessitates end-to-end QoS guarantees in terms of bandwidth, bounded delays and delay jitter. Q-Soft is independent of the network interface card and of the multimedia applications we run. The experimental results of our solution were obtained on a PC-Windows-based testbed consisting of a home network (wired or wireless) connected to the Internet via a residential gateway. The experimental results we have obtained provide evidence that our solution provides QoS service support for multimedia applications.

Efficient resource utilization through carrier grouping for half-duplex communication in GSM-based MEO mobile satellite networks

In the near future, existing terrestrial radio networks are envisioned to integrate with satellite systems in order to provide global coverage. In order to establish communication for both nonhand-held and hand-held user terminals, the radio link design must allow full- and half-duplex operation, respectively, where the latter is desirable when radiation power restrictions are imposed. In addition, due to user mobility and wireless channel volatility, sophisticated resource management is required, so as to enhance system capacity. However, a major inherent problem of the satellite link is propagation delay, which may lead to inefficient resource allocation and reduced spectral efficiency. We address the resource allocation problem that arises in the context of a medium-Earth-orbit (MEO) satellite system with half-duplex communication capabilities. MEO satellite systems are characterized by large propagation delays and large intrabeam delay variations, which are shown to result in resource consumption. We propose a channel classification scheme, in which the available carriers are partitioned into classes and each class is associated with a range of propagation delays to the satellite. The suggested infrastructure results in better channel utilization and reduced call blocking rate and can be implemented with low signaling load.

Minimizing cell delay variation in CRMA/ATM interworking

In wide area, networks, ATM is emerging as the predominant technology which provides flexible transmission and switching mechanism to accommodate a large variety of services. Though ATM can be used for LAN/MANs, at present it does not provide economical solution for LAN/MAN. A simple Cyclic-Reservation Multiple-Access (CRMA) protocol proposed in [1] can be used as a media access protocol for high-speed LAN and MAN on slotted unidirectional bus structure. While there is a need for interconnection of existing LAN/MAN networks, the evolution of new LAN/MAN protocols will depend on how easily and efficiently the protocol can interwork with the ATM. Under the normal CRMA protocol, ATM stations located in the CRMA network will experience large Cell Delay Variation (CDV) due to variable cycle lengths during access within the CRMA network. Also due to the cancellation mechanism incorporated within the CRMA protocol, the CDV increases. The CRMA access mechanism also forms bursts during access. This paper proposes a novel mechanism that minimizes the CDV in CRMA/ATM interworking by embedding fixed length cycles for the ATM traffic in the normal CRMA cycles of variable length. Another novel scheme is used which allocates CRMA slots uniformly to the ATM traffic within the fixed length cycles, thereby smoothing the ATM traffic. The simulation results show that the proposed scheme reduces the CDV and burstiness of ATM traffic to a great extent without significantly affecting the delay performance of the CRMA traffic.

083 Adaptive control with direct delay estimation

Abstract This paper addresses the challenging problem of controUing systems with unknown delay and offers a new solution by directly estimating the system delay using the Variable Regression Estimator (VRE). Pole-Placement control, Dahlin control and Generalized Predictive Control (GPC) are used with the Variable Regression Estimation and the resulting closed-loop performance enjoys fast adaptation and good regulation with minimum computations. With the VRE direct delay estimation, the GPC tuning parameters can adapt to delay changes in order to provide the same closed-loop performance over the range of delay variation. The VRE-based adaptive controller is successfully applied to an experimental setup with large delay variations.

Adaptive Control with Direct Delay Estimation

This paper addresses the challenging problem of controUing systems with unknown delay and offers a new solution by directly estimating the system delay using the Variable Regression Estimator (VRE). Pole-Placement control, Dahlin control and Generalized Predictive Control (GPC) are used with the Variable Regression Estimation and the resulting closed-loop performance enjoys fast adaptation and good regulation with minimum computations. With the VRE direct delay estimation, the GPC tuning parameters can adapt to delay changes in order to provide the same closed-loop performance over the range of delay variation. The VRE-based adaptive controller is successfully applied to an experimental setup with large delay variations.

Applications of amorphous magnetic-layers in surface-acoustic-wave devices

This paper reviews the theory and potential applications of magnetically variable delay lines and oscillators which employ a magnetostrictive film on a piezoelectric surface-acoustic-wave (SAW) substrate. Cases analyzed in detail indicate that the delay change arises mainly from a rotation of the magnetic moment from the films' easy axes toward the applied field direction; thus the interaction is essentially nondispersive. Use of amorphous metallic-glass overlays is particularly attractive because their high magnetostriction and low magnetic anisotropy makes a relatively large delay variation possible with a small change in bias field. Since the SAW velocity can be changed only by \sim .1 % or less with present film technology, applications are restricted to those where only a small frequency or delay adjustment is required. Two prototype examples are considered in detail--a variable delay line for steering an adaptive array antenna and a tunable resonator oscillator capable of tracking high speed Doppler targets. In both of these examples, the magnetic film/SAW substrate geometry is seen to be an attractive alternative to competitive approaches.